This invention relates to a novel process for preparing a live attenuated mumps virus vaccine which is effective for preventing epidemic parotitis (to be referred to as "mumps", hereinafter) infection.
Mumps is so contagious that kindergartens and primary schools are often closed during the prevalence thereof. Since those infected with mumps usually recover their health relatively quickly, mumps is considered a mild disease. However, since it is found that adults infected with mumps are attacked at testicle or ovary organs and as a result, become sterile, vaccines for preventing mumps infection are needed. Both live vaccine and inactivated vaccine had been investigated, but since inactivated vaccine cannot bring immunity lasting for a sufficient time after administration, it is now almost out of date. Live vaccine expected of prolonged immunity is now regarded feasible and a number of researches have been made on the preparation of live mumps virus vaccine. Exemplary of the culture host for mumps virus are amnion and chorio-allantoic membranes of embryonated hens' eggs and chicken embryo fibroblast cells. The article of Enders et al., Journal of Immunology, Vol. 54, 283-291 (1946) discloses the use of amniotic membranes which are ground and centrifuged. Only the pathogenicity of the virus for the monkey is indicated. The article of Henle et al., Journal of Immunology, Vol. 66, 579-594 (1951) discloses the virus of several allantoic passages. Smorodintsev et al. describes in Acta virol, 9, 240-247, (1965) that mumps virus is propagated in cultures of chicken embryo cells. However, no live vaccine has been prepared according to the teachings mentioned above. One live attenuated vaccine which has been used in practice is a live attenuated vaccine of Jeryl Lynn strain (see for example, The New England Journal of Medicine, Vol. 276, No. 5, 245-258 (1967)). Such live vaccines have several disadvantages in that the resultant antibody titre in blood is considerably lower than in the case of natural infection, the immunity may be retained for only a short time, and serial passage often attenuates the virus to an undesirable low level.
Therefore, vaccine having a high antibody production capacity is desired. Mumps virus generally tends to be relatively readily adapted and its immunogenecity tends to diminish rapidly. Factors of attenuation and immunogenecity retention thus appear to be alternative. Therefore, it is necessary to provide a process for the preparation of a live attenuated vaccine which is properly attenuated and retains continuing immunogenicity.